Something to add to the MVC known issues

There's an item that's been in the issue tracker for the past few months regarding
model binding directly to dictionaries in an action. The initial post got part of the issue but the root cause can result in a much more subtle bug, introducing false data into the application.

In both whether where it causes a runtime error or erroneous data it's a significant regression from previous versions of MVC but not well known and should probably be added to the list of known issues.